Once I liked where I was at I typically: Flatten the piece, Select all + Cut, undo the flatten, paste multiple layers and adjust each with different hues and colors. Then I just throw a layer mask on each and blend the masks.

Ah you've done it again, superb. Excellent details. One critique though for increased realism and detail, is that even in a highly radioactive and emissive nucleus of a nebula, this level of luminance and subsequent opacity are rare. Instead you should try to adopt more structured gasforms into the light, something to give shape and definition to the central cluster.